Involvement of tyrosine phosphorylation in the regulation of 5'-deiodinases in FRTL-5 rat thyroid cells and rat astrocytes

Recent studies suggest that protein tyrosine phosphorylation may play a role in the regulation of thyroid growth and function. In the present study, we used genistein, a specific inhibitor of tyrosine phosphorylation, to determine if tyrosine phosphorylation is involved in the regulation of type I 5'-deiodinase (5'D-I) expression in FRTL-5 cells and type II 5'-deiodinase (5'D-II) in rat astrocytes. Incubation of FRTL-5 cells with genistein (100 microM) for 3 days had no effect on cell viability as assessed by trypan blue exclusion. In TSH-deprived cells, incubation of FRTL-5 cells with genistein (100 microM) resulted in a modest, but not significant, decrease in 5'D-I activity. Incubation of FRTL-5 cells with TSH (100 microU/ml), Bu2cAMP (0.5 mM) or forskolin (1 microM) resulted in marked increases in 5'D-I activity. In the presence of genistein (100 microns), however, the TSH, Bu2cAMP and forskolin-induced increases in 5'D-I activity were completely inhibited. In Bu2cAMP-stimulated FRTL-5 cells, incubati...